1. Field
The invention is concerned with the pulverization and burning of solid fuels, such as coal, and with apparatus for accomplishing same.
2. State of the Art
Burning of pulverized coal in industrial burners has long been practiced. Initially, it was necessary to provide a dryer for the coal, a crusher, a grinder classifier, and storage for the coal as pulverized by the grinder. The classifier was required to separate oversize particles and return them to the grinder for pulverization. The pulverized coal was fed to the burner from storage.
The crushers used for the purpose were adapted from known types for disintegrating metallic ores in the extractive metallurgical industry and were complicated, high in cost, high in horsepower requirements, and were not able to operate under low load conditions, thereby requiring storage of the pulverized coal rather than direct feeding of the burner.
Later, smaller pulverizers were developed and are presently used to directly fire burners through duct systems by means of carrier streams of air. Oversize particles are returned to the pulverizer for further size reduction. To insure proper operation, it is necessary to either feed dry coal into the pulverizer or to dry wet or damp coal in the pulverizer by injecting hot air thereinto, which introduces additional structural and maintenance expenses and operative complications in that the system does not handle load changes very well.
Pulverization by attrition has been employed to a limited extent, but has required a source of considerable quantities of compressed air or steam at excessive expense.